IPv4 Only ARPA

ipv4only.arpa is a reserved special-use domain name in the Address and Routing Parameter Area (arpa) top-level domain, maintained by the Internet Assigned Numbers Authority (IANA) for standardized global network testing purposes. First delegated in 2013 per published IETF internet standards, the domain was created to support detection of dual-stack network connectivity, specifically to identify networks that can only route IPv4 traffic and fail to handle IPv6 transition protocols. The domain’s preconfigured DNS records resolve exclusively to IPv4 addresses, allowing operating systems, network devices, and software applications to test whether a network supports IPv6 connectivity by comparing results against its IPv6-only counterpart domain. This testing mechanism is a core part of the widely adopted Happy Eyeballs algorithm, which is used by most modern browsers and operating systems to improve connection speed for dual-stack networks by selecting the fastest available protocol automatically. The domain is not intended for public web access or end-user-facing content, and it does not resolve to public-facing websites or commercial services. It is one of several special-use arpa domains maintained to support core internet infrastructure operations, alongside other standardized test domains like example.com and example.org. Managed on behalf of the global internet community by ICANN, the domain’s configuration is standardized in IETF RFC documents to ensure consistent behavior across all network implementations worldwide. Its extremely high global traffic rank reflects the widespread automated testing that occurs from billions of internet-connected devices that check connectivity on a regular basis, making it one of the most frequently queried domains on the public internet.